    <div class="refentry" id="gl_FrontFacing">
      <div class="titlepage"></div>
      <div class="refnamediv">
        <h2>Name</h2>
        <p>gl_FrontFacing — indicates whether a primitive is front or back facing</p>
      </div>
      <div class="refsynopsisdiv">
        <h2>Declaration</h2>
        <code class="fieldsynopsis"><span class="modifier">in </span><span class="type">bool </span><span class="varname">gl_FrontFacing </span>;</code>
      </div>
      <div class="refsect1" id="description">
        <h2>Description</h2>
        <p>
            Available only in the fragment language, <code class="varname">gl_FrontFacing</code> is an input variable
            whose value is <code class="function">true</code> if the fragment belongs to a front-facing primitive and
            false otherwise. The determination of whether a triangle primitive is front-facing is made by
            examining the sign of the area of the triangle, including a possible reversal of this sign
            as controlled by <code class="varname">glFrontFace</code>. One way to compute this area is:
        </p>
        <p>
            <math overflow="scroll">
                <mi>a</mi><mo>=</mo><mfrac><mn>1</mn><mn>2</mn></mfrac>
                <msubsup>
                    <mo>∑</mo>
                    <mrow>
                        <mi>i</mi><mo>=</mo><mn>0</mn>
                    </mrow>
                    <mrow>
                        <mi>n</mi><mo>-</mo><mn>1</mn>
                    </mrow>
                </msubsup>
                <msubsup>
                    <mi>x</mi>
                    <mrow><mi>w</mi></mrow>
                    <mrow><mi>i</mi></mrow>
                </msubsup>
                <msubsup>
                    <mi>y</mi>
                    <mrow><mi>w</mi></mrow>
                    <mrow><mi>i</mi><mo>+</mo><mn>1</mn></mrow>
                </msubsup>
                <mo>-</mo>
                <msubsup>
                    <mi>x</mi>
                    <mrow><mi>w</mi></mrow>
                    <mrow><mi>i</mi><mo>+</mo><mn>1</mn></mrow>
                </msubsup>
                <msubsup>
                    <mi>y</mi>
                    <mrow><mi>w</mi></mrow>
                    <mrow><mi>i</mi></mrow>
                </msubsup>
            </math>
        </p>
        <p>
            where
            <math overflow="scroll">
                <msubsup>
                    <mi>x</mi>
                    <mrow><mi>w</mi></mrow>
                    <mrow><mi>i</mi></mrow>
                </msubsup>
            </math> and
            <math overflow="scroll">
                <msubsup>
                    <mi>y</mi>
                    <mrow><mi>w</mi></mrow>
                    <mrow><mi>i</mi></mrow>
                </msubsup>
            </math> are
            the x and y window coordinates of the <span class="emphasis"><em>i</em></span>th vertex of the n-vertex polygon.
        </p>
      </div>
      {$pipelinestall}{$examples}
      <div class="refsect1" id="versions">
        <h2>Version Support</h2>
        <div class="informaltable">
          <table style="border-collapse: collapse; border-top: 2px solid ; border-bottom: 2px solid ; border-left: 2px solid ; border-right: 2px solid ; ">
            <colgroup>
              <col style="text-align: left; "/>
              <col style="text-align: center; " class="firstvers"/>
              <col style="text-align: center; "/>
              <col style="text-align: center; " class="lastvers"/>
            </colgroup>
            <thead>
              <tr>
                <th style="text-align: left; border-right: 2px solid ; ">

            </th>
                <th style="text-align: center; border-bottom: 2px solid ; " colspan="3">
                <span class="bold"><strong>OpenGL ES Shading Language Version</strong></span>
            </th>
              </tr>
              <tr>
                <th style="text-align: left; border-right: 2px solid ; border-bottom: 2px solid ; ">
                <span class="bold"><strong>Variable Name</strong></span>
            </th>
                <th style="text-align: center; border-right: 2px solid ; border-bottom: 2px solid ; ">
                <span class="bold"><strong>1.00</strong></span>
            </th>
                <th style="text-align: center; border-right: 2px solid ; border-bottom: 2px solid ; ">
                <span class="bold"><strong>3.00</strong></span>
            </th>
                <th style="text-align: center; border-bottom: 2px solid ; ">
                <span class="bold"><strong>3.10</strong></span>
            </th>
              </tr>
            </thead>
            <tbody>
              <tr>
                <td style="text-align: left; border-right: 2px solid ; ">gl_FrontFacing</td>
                <td style="text-align: center; border-right: 2px solid ; ">✔</td>
                <td style="text-align: center; border-right: 2px solid ; ">✔</td>
                <td style="text-align: center; ">✔</td>
              </tr>
            </tbody>
          </table>
        </div>
      </div>
      <div class="refsect1" id="seealso">
        <h2>See Also</h2>
        <p>
            <a class="citerefentry" href="gl_FragCoord"><span class="citerefentry"><span class="refentrytitle">gl_FragCoord</span></span></a>
        </p>
      </div>
      <div class="refsect1" id="Copyright">
        <h2>Copyright</h2>
        <p>
            Copyright © 2011-2014 Khronos Group.
            This material may be distributed subject to the terms and conditions set forth in
            the Open Publication License, v 1.0, 8 June 1999.
            <a class="link" href="https://opencontent.org/openpub/" target="_top">https://opencontent.org/openpub/</a>.
        </p>
      </div>
    </div>
